Optical Time-Domain Reflectometers (OTDRs) are devices used for characterizing optical fibers, optical fiber links and/or optical fiber networks. A typical OTDR can have an optical pulse generator, an optical detector, a processor and a storage media incorporated therein.
During the characterisation of an optical fiber link, the OTDR launches optical pulses into the optical fiber link and monitors a time-dependent reflected signal associated with each of the optical pulses to provide an OTDR trace that can be stored in the storage media for further use. From the speed of light and the known optical fiber characteristics, the acquired reflected signal may be converted into a distance-dependent representation. It is known that the reflected signal is indicative of discrete reflections and/or backscattering that occur along the optical fiber link. Hence, the OTDR trace can be analysed in order to characterize localized and distributed loss and/or reflective events of the optical fiber link, for instance.
A problem with single-end OTDR measurements is the determination of insertion loss in cases where the link under test includes a concatenation of optical fibers. Small differences in fiber geometry between the different fiber segments induce small changes in the backscattering characteristics. This geometry mismatch between spliced fibers may cause an apparent “gain” or a drop in the backscattered light of OTDR measurements, which introduces a bias in the insertion loss measurement. For this reason, the Telecommunications Industry Association (TIA) recommends the use of bi-directional OTDR analysis to average the results of single-ended OTDR measurements and properly characterize multi-fiber links (test procedure EIA/TIA FOTP-61 “Measurement of Fiber or Cable Attenuation Using an OTDR”).
Backscattering characteristics are directly influenced by geometric factors such as core diameter, numerical aperture and index profile for example. Variability in geometric factors can be large when different types of fibers are connected together. However, even when all fiber segments are of the same fiber type, small geometric mismatches still may exist due to fiber manufacturing tolerances.
Although existing measurement techniques can be satisfactory to a certain degree, there remains room for improvement, particularly in terms of providing a single-ended OTDR optical loss measurement technique that is free from the aforementioned bias due to varying backscattering characteristics along the optical fiber link, and in terms of providing an optical loss measurement technique that reduces costs associated with bidirectional OTDR optical loss measurement techniques.